This invention relates to the retorting of oil shale under conditions to recover shale oil. More particularly, this invention relates to the retorting of oil shale under conditions such that the reaction products are not contaminated with products of combustion. Further, the retorting takes place under conditions such that energy is conserved and no outside fuel source is required.
The location of oil shale deposits is well known, and the processing of these deposits to recover valuable products is becoming more important in modern technology. The solid organic portion of oil shale is known as kerogen. When the shale is heated to an elevated temperature, the kerogen is decomposed by pyrolysis to give shale oil, light hydrocarbon gases and a carbonaceous residue. The technology of shale oil is well covered in Vol. 18 of "Kirk-Othmer Encyclopedia of Chemical Technology" (Interscience-John Wiley-New York).
A typical system for processing oil shale concerns a vertical retort having several sections, such as (a) a pre-heating section in which fresh shale is heated to retort temperature by any of several means, such as intermixing with hot spent shale or by direct heat transfer with hot combustion gases, (b) a retorting section in which the kerogen is pyrolyzed to give various products, (c) a combustion section in which combustible material, such as carbonaceous residue on the shale or the light hydrocarbon gases from the pyrolysis of the shale, are burned to furnish heat for the system, and (d) a spent shale section wherein some of the sensible heat is recovered from the hot spent shale.
Two of the major problems in this process concern the material handling of large amounts of shale and the exchange of heat between hot spent shale and fresh shale to give the necessary pyrolysis temperature. The prior art literature offers many proposed solutions for these problems, as discussed in the Kirk-Othmer article. However, these prior art methods typically have two disadvantages: (a) some of the kerogen material is used as fuel to provide heat for the pyrolysis, thus diminishing the yield of product per ton of shale, and (b) when the carbonaceous residue on the spent shale is burned to furnish heat for the process, the gaseous products of combustion and of carbonate decomposition are mixed with the pyrolysis products to give a low heating value (BTU/SCF) (kg. cal./m.sup.3) product.
These disadvantages are overcome in my process for the retorting of hydrocarbons from oil shale granules in a retorting vessel in which the oil shale is subjected to thermal decomposition of kerogen contained therein by the addition of heat, in the substantial absence of oxygen, and from which distillation reaction products are obtained substantially free of gaseous products of combustion and of carbonate decomposition, during the downward passage of shale through a plurality of physically separated zones in the vessel, the process comprising the steps of:
a. mixing fresh oil shale and hot spent shale in a hopper zone, PA1 b. removing gases from the shale mixture in a first low pressure zone, PA1 c. subjecting the shale mixture to an inert purge stream in a first purge zone, PA1 d. forming reaction products by thermal decomposition of kerogen in a reaction zone and removing and recovering said products, incidentally forming a carbonaceous residue on the shale, PA1 e. subjecting the retorted shale mixture to an inert purge stream in a second purge zone, PA1 f. removing gases from the retorted shale mixture in a second low pressure zone, and PA1 g. heating the retorted shale mixture by combustion of its carbonaceous residue. PA1 a. heat values are recovered from the hot spent shale, PA1 b. shale fines can be used in the process, PA1 c. the reaction products (from the reaction section) are undiluted by gaseous products of combustion and have an improved heating (BTU/SCF) (hg.cal./m.sup.3) value, PA1 d. the product from the reaction section is produced in more than 100% yield based on the Fischer assay, PA1 e. the fuel requirement per barrel of product is significantly negligible, PA1 f. the temperature of the reaction section is controlled so as to minimize carbonate decomposition in the shale, PA1 g. steam, used in the purge sections, is an essentially inert vapor and is easily condensible and removable from the other products, PA1 h. the net product yield per ton of shale is significantly higher than prior art processes, and PA1 i. the shale requirements per barrel of product are lower than prior art processes.
My invention also includes the apparatus containing the above-mentioned zones in the retorting vessel.
As a result of my invention, several advantages are noted:
These advantages are obtained by maintaining spent shale temperatures below 1400.degree.F. to prevent agglomeration of particles and to minimize use of expensive materials of construction.
The above-described process and the advantages of the invention are more fully understood by referring to the drawings.